1. Field of the Invention
The invention relates to an optical transmitting and/or receiving device, as used in optical telecommunications engineering. It relates in particular to a construction of an optical transmitting and or receiving device which is distinguished by favorable high-frequency properties. A preferred field of use is that of directly modulated semiconductor lasers in the frequency range greater than 5 GHz and associated receiving devices with a photodiode.
U.S. Pat. No. 6,271,049 B1 and EP 0 660 467 A1 disclose optical components with a laser chip as the light transmitter. The laser chip is arranged on a carrier consisting of silicon, which can be mounted on the base plate of a TO package. The contacting of the laser chip takes place via bonding wires.
The known optical components exhibit good high-frequency properties and data rates of up to about 2.5 Gbits/s. However, at data rates of 10 Gbits/s, rates which have by now been accomplished, the high-frequency (HF) performance deteriorates, since the impedance of the fed-in bonding wires plays an increasingly disadvantageous role with increasing frequency. It has been found that the HF properties of an optical transmitting and/or receiving device are substantially limited by the resultant inductance of the bonding wires, which at frequencies of about 10 Gbit/s is of the order of magnitude of 1 to 1.5 nH (1 nH=1 henry). On account of their inductance, the bonding wires provide a reactance, which is connected in series with the effective resistance of a semiconductor laser of typically 5 ohms, which leads to a change in impedance and an undesired signal reflection.
The problem is intensified by the fact that the appearance of the standard IEEE 802.3ae (10 Gbit Ethernet) and the associated requirements for very compact modules with low power consumption makes it likely that a 50 ohms impedance of the laser module is not viable in the long term for reasons of the power demand, so that it is desirable to change over to a smaller impedance of 20 to 30 ohms. With a smaller impedance of the driver system, however, the sensitivity of the construction to parasitic inductances increases, i.e. the reactance component caused by the inductance of the bonding wires becomes more noticeable and leads to an increased reflection of the high-frequency signal.
There is consequently a need for optical transmitting and receiving devices with which the sensitivity of the construction to parasitic inductances is reduced, to be precise in particular to an extent that the optical transmitting and/or receiving device can be provided with an impedance of 25 ohms.